Articles such as cigarettes and filter cigarettes are packaged in a bundle based on a given number. Conventionally, this packet includes inside packaging for maintaining the flavor quality of cigarettes and outside packaging for externally indicating the cigarette brand and the like. A cigarette packet, having undergone the inside packaging and outside packaging, is further externally wrapped in a covering film. A material that is formed of paper laminated with metal foil, such as tin foil or aluminum foil, having high quality maintaining function can be suitably used as the inner wrapper in which a cigarette bundle is to be wrapped. The material having the metal foil is so flexible that it can be folded with ease. After the material is folded, the material can naturally maintain its folded state.
Conventionally, therefore, a cigarette packaging machine uses a step of folding the inner wrapper, the step utilizing the properties of metal foil. After the inner wrapper is wound around the periphery of a cigarette bundle, in the cigarette packaging machine, movable folding claws are caused to advance into to-be-folded regions, which project sideways in the form of the square tube of the inner wrapper, according to predetermined steps of folding procedure. As this is done, the regions of the inner wrapper are folded. After one step of folding procedure is finished, the folding claws are quickly retracted to be ready for the next folding cycle. When the cigarette bundle is in the form of tiers of bales, for example, the to-be-folded regions of the inner wrapper that are located at opposite sides in the width direction of the cigarette bundle are referred to as lug portions. When each of the lug portions are folded, a pair of side flaps that are opposite to each other in the thickness direction of the cigarette bundle are formed, respectively. As this is done, the folding claws for folding the lug portions laterally advance toward the cigarette bundle, fold the lug portions along the end faces (aggregation of cigarette end faces or filter end faces) of the cigarette bundle, and then quickly retract from the end faces. When the aforesaid side flaps are folded in succession, thereafter, the inside packaging of the cigarette bundle is completed.
In the folding step described above, however, the lug portions are freed during the time interval that elapses from the instant that the lug portions of the inner wrapper are folded until the side flaps are folded, because of the retracting of the folding claws. In some cases, therefore, the lug portions are then apt to return to the state before the folding operation. If the extent of this return is extremely large, the side flaps that are once formed also get out of shape. Thereafter, neither the side flaps nor the lug poritons can be regularly folded, thus resulting in failure in inner wrapper folding.
Recently, moreover, recyclable materials have started to be used as packaging materials for cigarettes in consideration of environmental load. That is, there are increasing opportunities of using high-elasticity materials, such as deposited metal film, in place of conventional high-plasticity materials based on metal foil. If the deposited metal film, which is poor in plasticity, is used as an inner wrapper, in particular, the deposited metal film itself can hardly be expected naturally to maintain its folded state in the aforesaid folding process. If the deposited metal film is used as the inner wrapper, therefore, the inner wrapper folding operation in the cigarette packaging machine is liable to become more unstable.
In some cases, on the other hand, the wrapper folding operation may become unstable due to mechanical factors of the packaging machine, as well as to the characteristic factors of the packaging material. The fold wrapping of a product as well as the cigarette bundle comprises, for example, a step of folding a wrapper around a product and then folding end-flaps of the wrapper on the product, a step of folding lug portions of the wrapper that are caused to project sideways from the product, thereby forming a pair of side flaps at each side, and a step of successively folding the pair of side flaps.
According to a folding manner that is frequently used in the step of side flap folding, among other manners, the product is transported along folding lines of the side flaps, for example, and the side flaps are guided in being folded along folding guides in this process of transportation. Each folding guide has a guide surface that guides a side face of the product, and a folding edge is formed on the extreme end of the guide surface. The folding edge extends diagonally across the path of transportation of the product. As the product is transported, the side flap is guided by the folding edge and folded onto the side face of the product. If the product is transported sideways, for example, the pair of side flaps, upper and lower, are formed beside the product as the lug portions of the wrapper are folded. When the upper side flap is guided in being folded by means of the folding guide, thereafter, a difference in level corresponding to the length of projection of the upper side flap is secured between the starting and terminal ends of the folding edge. The starting end is located slightly above the upper side flap. As the product is transported, therefore, the upper side flap engages the folding edge and is folded down along the folding edge during its passage. When the upper side flap passes the terminal end of the folding edge, the upper side flap is held between the product and the guide surface, whereupon folding the upper side flap is finished.
According to the folding method described above, the lateral force of transportation is supposed to be converted into a downward force of depression when the upper side flap of the wrapper is slid relatively to the folding edge as the product is transported. This force of depression can cause the upper side flap to be laid over the sided face of the product so that the upper side flap can be brought gradually into intimate contact with the side face of the product, its proximal end portion first.
If the coefficient of friction between the wrapper and the folding edge is extremely high, for example, however, the folding edge is subjected to an excessive resistance opposite to the direction of movement of the wrapper, so that the side flap is then dragged heavily. If the wrapper lacks in rigidity depending on its material, the force received from the folding edge may be concentrated only on a part of the side flap and fail to be effectively transmitted as a force to bend the side flap in some cases. In these circumstances, it is hard to fold the side flap accurately along its regular crease.
With the recent improvement of the production capacity of cigarette manufacturing machines, moreover, the cigarette packaging machine, for example, has started to require shorter packaging cycles. Thus, a step of wrapping a cigarette bundle in an inner wrapper, for example, requires development of technique for folding side flaps while transporting the cigarette bundle at a higher speed in a shorter interval of transportation.